1. Field of the Invention
The present invention relates to a method and apparatus for detecting the dynamic variation of, e.g., ultrasonic waves propagating through an object to be inspected. Further, the present invention relates to an ultrasonic diagnostic apparatus provided with such an ultrasonic detection apparatus.
2. Description of a Related Art
A typical ultrasonic diagnostic apparatus performing the so-called ultrasonic echo observation, etc., uses an ultrasonic sensor unit (probe) made of a piezoelectric material represented by PZT (Pb (lead) zirconate titanate).
FIGS. 18A and 18B diagrammatically show the structure of the conventional probe. FIG. 18A is a general perspective view of the probe and FIG. 18B is an enlarged perspective view of an array vibrator included in the probe.
Referring to FIG. 18A, a probe 301 is generally thin box-shaped and has a rectangular probe face 302. The probe face 302 is abutted against the human body to transmit ultrasonic waves and receive ultrasonic echoes returned from a far site within the human body. A cable 307 is connected to the top of the probe 301, for sending ultrasonic transmission and reception signals therethrough.
A comb-shaped array vibrator 303 is present in the probe face 302. The array vibrator 303 serves both as an ultrasonic oscillator and an ultrasonic receiver. Referring to FIG. 18B, the array vibrator 303 includes a multiplicity of (e.g., 256) comb-tooth-shaped discrete vibrators 305 (e.g., 0.2 mm wide, 20 mm long) arrayed in a thin (e.g., 0.2 mm to 0.3 mm thick) PZT strip with a multiplicity of slits 306 (e.g., 0.1 mm wide).
Each discrete vibrator 305 is formed with an electrode having a signal line connected thereto. The array vibrator 303 has a front surface (lower side in the diagram), to which are adhered an acoustic lens layer and a matching layer which are made of a resin material including rubber, and has a reverse surface to which is adhered a packing material. The acoustic lens layer contributes to an improvement in the transmitted ultrasonic wave focusing properties. The matching layer serves to enhance the ultrasonic wave transmission efficiency. The packing material has a function to retain the vibrator and puts earlier termination to the vibration of the vibrator.
It is to be noted that such ultrasonic probe and ultrasonic diagnostic apparatus are described in larger detail in xe2x80x9cUltrasonic Observation Method and Diagnostic Methodxe2x80x9d published by Toyo Publisher and xe2x80x9cFundamental Ultrasonic Medicinexe2x80x9d published by Ishiyaku Publisher.
By the way, in the field of the ultrasonic diagnosis, three-dimensional data collection is desired to obtain more detailed biological information. In order to realize this, it is required to provide ultrasonic detectors (ultrasonic sensors) in the form of a two-dimensional array. However, the above-mentioned PZT makes difficult further miniaturization and device integration exceeding the present state due to the following reasons. That is, the PZT material (ceramics) processing technology is coming nearer to its limitation, such that further miniaturization may result in an extreme reduction of the processing yield. The number of wires may also increase, which leads to increase electrical impedance of the wiring. The crosstalk may also increase between the devices (discrete vibrators). For these reasons, it is considered to be difficult in the state of the art to realize the two-dimensional array probe using PZT.
ULTRASONIC IMAGING 20, 1-15 (1998) carries a thesis titled xe2x80x9cProgress in Two-Dimensional Arrays for Real-Time Volumetric Imagingxe2x80x9d by E. D. Light, et. al. of University of Duke. This document discloses a probe having a two-dimensional array for the PZT ultrasonic sensor. At the same time, however, this reads as follows. xe2x80x9cTo obtain images of a similar quality, the number of elements of the two-dimensional array needs to be 128xc3x97128=16,384. However, formation of such a multiplicity of RF channels may be infeasible in near future due to its complexity and increased costs. It may also be extremely difficult to densely connect such a multiplicity of elements to one anotherxe2x80x9d (page 2, lines 14-18).
On the other hand, sensors utilizing optical fibers are also available as the ultrasonic sensors not using the piezoelectric material such as PZT. Such optical fiber ultrasonic sensors are suitable for the measurement at places greatly influenced by magnetic field or at minute sites.
J. Acoust. Soc. Am. 93(2), February 1993, pp. 1182-1191 bears a thesis titled xe2x80x9cOptical transducer for reception of ultrasonic wavesxe2x80x9d by Partick J. Phillips, et. al. This document proposes an ultrasonic-optical transducer utilizing the fact that the intensity of near-field light (evanescent light) in the vicinity of the interface where light is totally reflected varies because of the presence of an object in the near-field. The document also discloses determining the one-dimensional distribution of sound pressure of the ultrasonic waves by scanning the light beam spot over the total reflection interface.
However, the thesis by Phillips, et. al. does not include any specific disclosure on the method of executing the detection of the two-dimensional distribution of ultrasonic wave sound pressure, without making beam scanning, in real time which is required for the medical image diagnostic apparatus.
The present invention was conceived in view of the above deficiencies. It is therefore the object of the present invention to provide an ultrasonic detection method, an ultrasonic detection apparatus and an ultrasonic diagnostic apparatus which are suited for real-time collection of three-dimensional ultrasonic data.
In order to solve the above problems, according to the present invention there is provided an ultrasonic detection method comprising the steps of: (a) introducing a light beam into an ultrasonic-optical transducer including a first optical layer and a second optical layer which define a gap having a predetermined length therebetween from a side of the first optical layer such that the light beam is totally reflected at an interface between the first optical layer and the gap to obtain the reflected light beam, the introduced light beam having a wavelength larger than the predetermined length of the gap; (b) applying ultrasonic waves onto the ultrasonic-optical transducer from a side of the second optical layer such that the second optical layer resiliently deforms to thereby vary intensity of light leaking from the first optical layer via the gap into the second optical layer;
(c) two-dimensionally detecting distribution of intensity of the reflected light beam which varies depending on variation of the intensity of the light leaking from the first optical layer via the gap into the second optical layer; and (d) two-dimensionally obtaining distribution of sound pressure of the ultrasonic waves applied on the second optical layer on the basis of the distribution of intensity of the reflected light beam detected at step (c).
According to the present invention there is provided an ultrasonic detection apparatus comprising: an ultrasonic-optical transducer including a first optical layer and a second optical layer which define a gap having a predetermined length therebetween, the second optical layer being resiliently deformed such that the length of the gap varies when ultrasonic waves are applied from a side of the second optical layer; means for introducing a light beam having a wavelength larger than the predetermined length of the gap into the ultrasonic-optical transducer from a side of the first optical layer such that the light beam is totally reflected at an interface between the first optical layer and the gap; detecting means for two-dimensionally detecting distribution of intensity of the reflected light beam which varies depending on variation of intensity of light leaking from the first optical layer via the gap into the second optical layer; and signal processing means for two-dimensionally obtaining distribution of sound pressure of the ultrasonic waves applied on the second optical layer on the basis of the distribution of intensity of the reflected light beam detected by the detecting means.
According to the present invention there is provided an ultrasonic diagnostic apparatus comprising: a transmission unit for transmitting ultrasonic waves to an object; a detection unit having: an ultrasonic-optical transducer including a first optical layer and a second optical layer which define a gap having a predetermined length therebetween, the second optical layer being resiliently deformed such that the length of the gap varies when ultrasonic waves are applied from a side of the second optical layer; means for introducing a light beam having a wavelength larger than the predetermined length of the gap into the ultrasonic-optical transducer from a side of the first optical layer such that the light beam is totally reflected at an interface between the first optical layer and the gap; and detecting means for two-dimensionally detecting distribution of intensity of the reflected light beam which varies depending on variation of intensity of light leaking from the first optical layer via the gap into the second optical layer; a signal processing unit for two-dimensionally obtaining distribution of sound pressure of the ultrasonic waves applied on the second optical layer on the basis of the distribution of intensity of the reflected light beam detected by the detecting means; and a display unit for displaying an image on the basis of a detection signal output from the signal processing unit.